Evil (part I)

"Concerning this thing, my lords, you now all know enough for the understanding of our plight, and of Sauron's. If he regains it, your valour is vain, and his victory will be swift and complete: so complete that now can foresee the end of it while this world lasts. If it is destroyed, then he will fall; and his fall will be so low that none can foresee his arising ever again. For he will lose the best part of the strength that was native to him in his beginning, and all that was made or begun with that power will crumble, and he will be maimed for ever, becoming a mere spirit of malice that gnaws itself in the shadows, but cannot again grow or take shape. And so a great evil of this world will be removed."

Gandalf in The Last Debate - The Return of the King
The Lord of the Rings (1955) - JRR Tolkien
HarperCollins